This invention relates to cameras having electronically controlled shutters, and more particularly to a type thereof wherein a voltage check circuit is provided within the shutter control circuit, and the operation of the camera is inhibited by cutting the electric current flowing through the shutter holding magnet when the voltage of the power source is reduced below the level which will sustain normal operation of the photometric and operational circuitry.
Heretofore, various examples of a camera having an electronically controlled shutter are known, wherein the shutter operation is inhibited to prevent erroneous operation of the camera or degradation in the photograph when there is an omission or a decrease in the power of the power source for the control circuit. One such example can be found in Japanese Patent Laid-Open No. 46130/1975.
Such a type of camera is advantageous in that when the operation of the magnet becomes erratic, the camera is made inoperative and the possibility of taking inferior photographs as the result of erratic operation is thereby eliminated. However, in the operation of such cameras, a range of voltage causing erroneous operation exists between the normal operational voltage for the electronic circuit and a voltage at which the camera is made inoperative for the purpose of alarming against the erratic operation. Within the latter range successful photography is not guaranteed. This is because the voltage at which the magnet can hold the sustain rear shutter screen open is not equal to the operational voltage of the photometric and operational electronic circuit, and furthermore cannot be made equal thereto because of a wide variety in the holding characteristic of individual magnets and the temperature variation of the characteristic of each magnet. For his reason, the minimum voltage for holding open the rear shutter screen by the magnet is ordinarily preset to a value below that required to maintain normal operation of the photometric and operational circuitry.